Meccano mechanisms incorporating electronics
By Gilbert Ghyselbrecht

In response to the call for some practical examples of the uses of electronic circuits in Meccano models, I have developed a system called the Meccano Relay Board which provides modellers with several simple means of controlling their motors. In addition, I have designed mechanisms which make use of this board, and these mechanisms will be the main subject of this article.

The relay board

My relay board is in the first place intended to work with one or two of my slotted opto-switch modules (see issue 10 of EiM), but it is also possible to use micro switches.

The circuit is built on a printed circuit board with the dimensions of a 5 x 7 hole Meccano plate. Connections to the board are made using screw terminals, and the power supply for the board is 12V DC.

The motor to be controlled is connected to a relay on the board which has two individual N.O. - N.C. contacts with a switch rating of 5A 250V AC.

The board can be configured by a jumper link to work in one of three possible modes:

  • Mode 1 - TOGGLE
    Activating Sensor 1 will switch the relay on and activating Sensor 2 will switch it off.
     

  • Mode 2 - MONOSTABLE
    When activating Sensor 1 or 2 the relay will switch on and stay on for an adjustable time from 0.1 to 10 seconds.
     

  • Mode 3 - ON – OFF
    When activating Sensor 1 or Sensor 2 or both, the relay will switch on.

The Meccano Relay Board.  Click here to enlarge this photo...
 

Mechanism 1

A crank (Meccano part 62) is fixed to an axle rod, connected with or without gears, to the driving motor of the model. A push button is used to start the movement. The crank turns and will interrupt the light beam in an opto-switch. This will stop the motor. The relay board is here used in mode 1 (toggle mode).

When using the relay board in mode 2 (monostable), with the same mechanism, the motor will turn intermittently. The stop time is adjustable.

Mechanism 1.  Click here to enlarge this photo...
Mechanism 1 and the Relay Board.  Click here to enlarge this photo...

 

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Figure 1: Wiring the relay board for Mechanism 1

Mechanism 2

A bush wheel (Meccano part 24) is taped to cardboard and one or more holes are left open. The wheel turns in the gap of the opto-switch. The sensor is connected to a relay board configured in mode 2 (time delay). The output of the relay can be used to switch other motors or lamps etc.

Mechanism 2.  Click here to enlarge this photo...
A close-up of mechanism 2.  Click here to enlarge this photo...

 

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Figure 2: Wiring the relay board for Mechanism 2

Mechanism 3

Flic-Flac!  Here I use two opto-switches connected to a relay board in mode 1 (toggle). The motor is connected to the relay output and turns right and left, and right and …

Mechanism 3.  Click here to enlarge this photo...
Mechanism 3.  Click here to enlarge this photo...

 

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Figure 3: Wiring the relay board for Mechanism 3

Building the relay board

The circuit diagram of the relay board is shown in figure 4, and a parts list is given in the Shopping List at the end of this page.  You could build the circuit on stripboard, but a better solution is to etch a PCB if you have the facilities available to do this.  Click here to download he PCB layout as an Adobe Acrobat file.  Alternatively, the Meccano Relay Board can be purchased from the Electronics in Meccano Circuits Shop (see the end of the article).

Figure 4: Circuit diagram of the Meccano Relay Board.  Click here to enlarge this diagram...
Figure 4:
Circuit diagram of the
Meccano Relay Board

Figure 5: Circuit layout on the PCB.  Click here to enlarge this diagram...
Figure 5:
Component layout on the PCB

Solder the components to the board in the following order:

  1. The two wire links.  The longest one runs under the 555 IC socket (U2) and so must be placed before this IC.

  2. Diodes D1 and D3.  Make sure their orientation is correct.

  3. Resistors R1 - R6, R8, R9.  For R1 and R2, use the holes that suit the resistor size.

  4. IC sockets for U1 and U2.  Make sure the notch points to the left in both cases.  Do not insert the ICs until the board is complete.

  5. The six jumper pins.

  6. Capacitors C1 - C4.  For C1 and C2, use the holes that suit the capacitor size.

  7. 3mm LED D2.  Make sure its orientation is correct.

  8. Transistor T1.  Make sure its orientation is correct.  The black mark shows where the tab of a BFY51 transistor should be should you need to use this transistor type instead of a BC517 (see the note in the Shopping List).

  9. Capacitors C5 - C7.  Make sure their orientation is correct.

  10. Cermet resistor R7.

  11. Terminal blocks.

  12. Regulator U3.  Make sure the front (with the writing) is facing towards C6.

  13. 12V DPDT relay.

  14. Insert the ICs U1 and U2.

The Electronics in Meccano Circuits Shop Buy the Meccano Relay Board and Opto Switch Modules from the Electronics in Meccano Circuits Shop

Click here for details

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A remote control system

The receiver and transmitter modulesThis article and its concluding part in issue 12 of Electronics in Meccano, will show how you can construct a simple remote control system capable of controlling two DC motors.

Figure 6 shows a block diagram of a generic remote control system. The comments beside each block give details of the components we will be using in this design. All the components are available from Maplin and are fairly inexpensive.

This part of the article will focus on the radio transmitter and receiver blocks. The transmitter and receiver modules we will be using send a single bit of data (i.e. on and off) over a short range using amplitude modulation (AM) with a carrier frequency of 418MHz. This frequency is generally used for remote control applications such as car alarms and garage door opening systems, and is therefore licence exempt.

Both modules are made by RF Solutions and have no adjustable parts, meaning you can just connect them up and they should work.

Figure 6: A block diagram of a remote control system and the components used in this design

Figure 6: A block diagram of a remote control system and the components used in this design.
Click to enlarge this figure.

The transmitter module

The transmitter module (shown above right) has only two pins and looks similar to a capacitor. When connected up as shown in figure 7a, it will transmit when the Data Input is taken high (5V). When you don’t want it to transmit, the Data Input should be taken low (0V).

The Data Input voltage does not have to be 5V - it can be from 2.5V up to 13.1V - but if you do want to change it you would also have to change the value of the resistor Rd, which means you will have to get the datasheet for the module and do a few calculations. We will keep the voltage as 5V since we will need a 5V supply for the encoder block in the second part of this article.

Click here to read this datasheet in Adobe Acrobat format AM Transmitter Module Datasheet
60Kb

The receiver module

The receiver module (shown above left) looks more complicated than the transmitter module since it has 10 connections on a 38mm x 14mm printed circuit board. However, four of these are for the +5V power supply, and three are for the 0V power supply, which leaves one for the antenna, and one for the Data Output. The Data Output supplies enough current to light an LED, or switch on the Darlington Pair circuit from issue 8 of EiM if you want to control a motor.

The module does need to have a regulated 5V power supply, so you will need a 7805 regulator and a battery capable of supplying over 6V to it.

Click here to read this datasheet in Adobe Acrobat format AM Receiver Module Datasheet
68Kb

The system as it stands is capable of switching one motor on and off, with rotation in one direction only. The encoder and decoder blocks will enable two motors to be switched on and off, and can control their direction.

Figure 7: Connection diagrams for (7a) the transmitter module, and (7b) the receiver module

Figure 7: Connection diagrams for the transmitter and receiver modules.
Click to enlarge this figure.

Continued in: A remote control system part 2

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The infra-red experience!

Dear Editor,

My daughter Jessie and I have been experimenting for some time with fitting the Meccano Infra-red System (IRS) to our models.

We have three IRS sets and each seems to have a “personality” of its own. They are temperamental to say the least. We have found that they do not like rechargeable batteries, especially NiCads and especially the handsets. The handsets perform most reliably with something like new Duracells.

Evidently, the handsets can be “tuned” - there is a potentiometer in there somewhere that can be adjusted. Does anyone know how to do this and how to test that the adjustment is correct? The tamper-proof screw drivers for the triangular-holed screws can be obtained from Maplin, so we have been told.

We have also found that the relays (four, one for each motor, forward and reverse) inside the main receiver box tend to stick sometimes—it might be just one that plays up whilst the other three are fine. Is this battery trouble or what? One of our members (NELMC) has had his IRS apart and re-made all the soldered joints, which has improved its operation.

Lastly, we come to the driving force of a model, the motors. We have found that, if using the IRS in a model car, you cannot steer as you drive or vice versa, i.e. you can’t operate both motors at the same time. Obviously, with a nice free running vehicle running on a smooth surface, one can coast it whilst steering with the steering motor. We are told that the sensors can only receive/recognise one signal at a time. Is this the case or are our sensors at fault?

We find that standard Meccano type models are too heavy for this system and everything needs gearing down so much so that progress is very ponderous. Even the Action Control models designed for this system seem reluctant to move the further they get from one, even on a smooth surface. The operational range is supposed to be about 12 feet - in reality, it is often down to 6 feet or even 3 feet.

These are models that we have “tweaked” to improve the steering and gearing to make them operate more freely. The two motors are operated from the same 4xAA battery pack (i.e. 6V max.). I was wondering whether it would be possible to use a 6xAA (9V) battery pack in order to give the motors a bit more power.

Just after Christmas I had to return two of these Action Control sets to Savacentre Beckton. I had purchased them before Christmas for my young daughter to use. They were on offer at £19.99 - about all they are really worth as far as I am concerned. The IRS did not work in either of the sets. I phoned the store and arranged for replacements. As I lived miles away from the store, I decided to test any sets before leaving the store. Thus I took along my most reliable IRS as a “control”. Together with an assistant I tried six or more sets off the shelf. None of them worked. I cross-checked handsets against receivers and found about 50% had handset trouble and 50% had problems with the relays in the receiver. We were using brand new Duracell batteries from the store. I suppose this is a case of caveat emptor! I came away from the store with a refund.

Anyway, these are our experiences, our findings, suggestions, and disappointments with the Meccano Infra-red System. If anyone has any other experiences, suggestions or help to get this system functioning in a satisfactory way, perhaps they could publish them for the benefit of all through Tim’s august publication.

Mike Tebbutt
Epping, Essex


Title: Shopping ListThe following lists the electrical parts that are discussed in the articles. Prices and order codes given are taken from the current Maplin catalogue, which is the probably best source of electronic components for the hobbyist in the UK.

If you have access to a company account with Rapid Electronics or RS Electronics you may find these companies are cheaper.

Meccano mechanisms incorporating electronics
 
Parts required to build the Meccano Relay Board on PCB.
Maplin Order Code Price Page
R1, R2, R3, R5 4 x 68kW 0.6W metal film resistor M68K 7p 221
R4, R8 2 x 1kW 0.6W metal film resistor M1K 7p 221
R6, R9 2 x 10kW 0.6W metal film resistor M10K 7p 221
R7 1 x 100kW 18-turn cermet resistor WR51F 79p 225
C1, C3, C4 3 x 10nF 50V ceramic disc capacitor (same as 0.01uF)  BX00A 7p 88
C2 1 x 470pF 50V metallised ceramic plate capacitor WX64U 13p 89
C5, C6 2 x 100mF 63V radial electrolytic capacitor WH39N 39p 93
C7 1 x 10mF 16V low profile electrolytic capacitor AT98G 15p 93
D1 1 x 1N4148 signal diode QL80B 8p 246
D2 1 x 3mm green LED WL33L 8p 181
D3 1 x 1N4001 rectifier diode QL73Q 5p 246
T1 1 x BC517 (not available from Maplin)
Suitable alternatives with the same package are BCX38, TIPP110, and TIPP112.  A BFY51, which is available from Maplin has a larger package and may be used instead of the BC517 if the value of resistor R6 is also changed from 10k
W to 3.3kW (Maplin order code M3K3).
QF28F 49p 247
U1 1 x 4001 quad NOR logic gate IC QX01B 39p 250
U2 1 x 555 timer IC QH66W 29p 292
U3 1 x 78L05 0.1A regulator QL26D 39p 269
1 x 12V 5A DPDT relay QC95D £2.69 217
1 x 8-pin IC socket BL17T 14p 304
1 x 14-pin IC socket BL18U 19p 304
1 x 2.54mm miniature pin jumper UL71N 19p 124
1 x 2.54mm pin strip (36 pins - cut to size) JW59P 79p 129
2 x 3-way PCB terminal block NF08J 39p 132
1 x 4-way PCB terminal block NF09K 49p 132
1 x 6-way PCB terminal block NF10L 69p 132
A remote control system
 
Parts required to build the transmitter block of the remote control system:
Maplin Order Code Price Page
560W 0.6W metal film resistor M560R 7p 221
22pF variable tuning capacitor WL70M 99p 96
220pF metallised ceramic plate capacitor WX60Q 13p 89
418MHz transmitter module GT39N £9.99 697
 
Parts required to build the transmitter block of the remote control system:
Maplin Order Code Price Page
2 x 0.1mF metallised polyester film capacitor BX76H 15p 91
7805 regulator CH35Q 39p 270
418MHz receiver module CR75S £9.99 697

Maplin charge £2.50 for delivery on orders under £30.00 ex VAT.
Prices are taken from the September 2000 - August 2001 Maplin catalogue, and include VAT at 17.5%

Contact their order line on 0870 264 6000 or visit one of their shops.
Their customer service line is 0870 264 6002 and they have a website at www.maplin.co.uk where on-line ordering is available.

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Electronics in Meccano April 2001 -- Issue 11

Edited by Tim Surtell
E-mail: timsurtell@eleinmec.freeserve.co.uk


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